Several types of implantable medical devices require electricity to operate. Implantable medical devices such as distraction or adjustment devices can be implanted in subjects to correct structural malformations or injuries to the skeletal and muscular system. Many different types of distraction devices are known. For examples, devices are known in the art for the correction of spinal sclerosis, stenosis and other spinal conditions (e.g. U.S. Pat. No. 7,615,052, U.S. 2010/0262247), for lengthening long bones of the arm or legs (e.g. U.S. Pat. Nos. 6,245,075, 6,383,185), treatment of micrognathia, and for craniofacial correction (e.g. U.S. 2009/0192514). Many apparatus design elements are known for the manufacture of distraction devices including devices designed for promoting osteogenesis over an extended time period of treatment.
Due to the slow growth rate of osseous tissue, distraction devices typically operate through the application of small changes in force over time to correct bone structure. For example, a distraction device can have two or more attachment points for connecting to bone in a subject and a distraction or adjustment mechanism to adjust a distance between the two attachment points over time. In a typical treatment, each adjustment of the distraction device can be 5 mm or less in distance due to the slow growth rate of osseous tissue. Numerous adjustments are made to the distraction device, sometimes over several months, with the distraction device implanted below the dermis and often the musculature of the subject.
Early distraction devices contained a frame or other scaffolding located outside of the subject's tissues with one or more pins extending through the subject's skin and connected to the bone or a separate distraction device. Adjustments to the frame were made periodically to affect adjustment of the distraction device. Hence, the implanted distraction device was adjustable over the extended time course of treatment despite the location of actual attachment to the bone being located under the skin and musculature. However, the external frame of the device is often heavy and cumbersome to the patient. Further, the pins or other transcutaneous elements extending from the external environment into the tissue of the patient are a source for infection and scarring.
Mandibular distraction is a treatment for the correction of micrognathia, and such treatment is frequently utilized for micrognathism in children. With children in particular, there are issues associated with current distraction solutions. The expansion of mandibular distraction devices is generally actuated via an input of mechanical force by an operator, typically a parent, however there remains the possibility of the child actuating the mechanism themselves, accidental or otherwise. Additionally, there are emotional aspects associated with the unaesthetic appearance of mandibular distraction devices protruding from the skin. A completely implanted device would be particularly useful for addressing these concerns, primarily in children, and to a lesser extent in adults. However, an implanted solution presents the problem of transmitting the energy necessary to actuate the device.
To avoid the complications caused by an external frame, systems where the entire device is implanted into the patient have been developed. In some instances, the device has a mechanical action that can be activated through external manipulation of the subject; however, operation of such devices is difficult. Other devices require the subject to be sedated for surgery and an incision made to gain access to the implanted device for the purpose of manual adjustment of the implant. The subject is undesirably subjected to risk of infection and complications from sedation.
Completely implantable devices without transcutaneous elements require a source of power other than direct mechanical power provided by a medical professional performing an adjustment. More recent devices include the implantation of a motor and power source, such as a battery, into the patient. For example, WO 92/22268 teaches a device where a motor, battery, and pre-programmed control components are implanted, where the control components carry out a preset series of instructions to adjust the distraction device. However, the course of treatment cannot be modified after the device is implanted. To overcome this limitation, other devices have been developed that contain an RF receiver to receive instructions from an external controller, for example, US 2009/0192514. However, such systems require capacitors and other electrical components to be implanted within a patient, with the capacitors serving as the sole power source over an extended course of treatment. The quality and duration of treatment deliverable by such systems is limited by the implanted power source. Further, there are risks inherent to implanting energized electrical components within a patient. Additionally, RF control signals can be obstructed in the cases of obese patients.
Some systems have addressed the limitation of the amount of total power capacity of an implantable battery through the use of a rechargeable battery or a motor operable by a current induced from an applied magnetic field (e.g. U.S. Pat. No. 7,135,022, U.S. 2010/0262247). The amount of energy that can be practically delivered by induction is limited. Further, batteries suitable for implantation are limited in their rate of current discharge even if rechargeable. Hence, the amount of mechanical work that can be performed to affect the adjustment is limited. Further, batteries and capacitors contain toxic materials that represent an elevated risk when implanted into the patient.
Systems which directly connect an electrical source to an implanted medical device conduct electricity at low voltages and currents but are generally restricted to data transmission to and from the medical device. The capacity for electrical transmission of such systems is unsuitable for operation of medical devices having high electrical operating requirements.
Due to the limitations discussed above, the scope of implanted medical devices requiring electricity is restricted to data transmission to and from devices, which require only small operating voltages and currents. Additionally, the types of therapies deliverable to a patient by an electrically operated implanted medical device is similarly limited due to the low power transmission capacities of induction and/or battery operated systems. Therapies and devices which might require a comparably higher degree of electrical transmission to an implanted device for treatment undesirably pose risks of electrical shock to both patients and operators.
Still other devices have contemplated the use of a magnetic field to affect adjustment of an implanted distraction device by interaction with magnetic components included with the implanted part of the device (e.g. U.S. 2009/0192514, U.S. 2010/0262239, WO 2009/060427, WO 2011/035308). However, the amount of torque force that can be developed by manipulation of an external magnetic field is often limited in practice leading to a similar limitation compared to devices including an implanted battery. As such, there is a need for a system that can deliver a higher voltage and current to implanted devices than currently available systems, without posing the risk of electric shock to patients and operators.